The public has increasingly been concerned about possible health hazards due to low frequency radiation emanating from electrical and electronic devices, as well as the associated electrical power lines and distribution equipment. One concern has been focused on the effects of long-term exposure to magnetic fields generated by high powered, alternating current (AC) transmission lines, and whether or not they can cause cancer. This concern has resulted in certain studies of the problem, such as the case-controlled study undertaken by the Karolinska Institute, in Stockholm, Sweden, between 1960 and 1985. That study found some correlation between childhood leukemia and adult myeliod leukemia and magnetic flux densities exceeding the 200-300 nanotesla range especially in individuals living within 300 meters of high voltage powerlines. See, for example, Ahlbomn Feychting, "Magnetic Fields and Cancer in People Residing Near Swedish High Voltage Power Lines," Karolinska Institute, IMM-Rapport, June 1992.
Another concern relates to the emissions of the electrical and electronic devices themselves, and particularly devices which generate electromagnetic energy at frequencies higher than the AC power lines, such as the cathode ray tubes (CRTs) used in television sets and the visual display units (VDUs) associated with computers. Among the symptoms thought to be related to prolonged exposure to the radiation generated by such devices are increased risk of miscarriage among pregnant women, and allergic reactions to the skin and eye, although conclusive scientific proof associating such symptoms with prolonged exposure to CRTs is lacking.
Due to this increased anxiety among the public at large, a number of governments and other institutions have begun to establish systems for nonmandatory testing of CRTs and other equipment.
For example, the Swedish government has established its "Alternating Electromagnetic Field Exposure Guidelines", MPR 1990:8. The electromagnetic emission characteristics established by these nonmandatory guidelines fall into two frequency bands of interest. A first, extremely low frequency (ELF) band extends from approximately five hertz to two kilohertz (kHz), and is primarily concerned with fields generated at the frequency of electric power lines. The suggested limit for acceptable magnetic field flux densities is 250 nanoteslas root mean square (rms) in the ELF band.
A second, very low frequency (VLF) band, ranges from approximately two kHz to 400 kHz, and flux densities greater than 25 nanoteslas (rms) are considered to exceed the guidelines. Electromagnetic energy in the VLF band is primarily generated by the vertical and horizontal retrace circuits in electronic devices, principally CRTs.
In practice, we have found that a number of appliances and electronic devices in common use in the home as well as in the office may generate enough electromagnetic energy to result in exposure to flux densities greater than that specified by the Swedish government guidelines. This is especially true for devices which are meant to be held in close proximity to the body during their use, such as electric razors, hair dryers, curling irons and the like.
Ungrounded or otherwise faulty electrical wiring systems may cause unbalanced return currents that also generate potentially harmful electric fields. In fact, instances have been observed in which an improperly grounded home wiring system generates ELF fields in excess of 250 nanoteslas in the home next door, even when the adjacent home itself has a properly grounded electrical system.
Traditionally, ELF and VLF radiation has been measured with precision scientific instruments such as laboratory gausmeters. These instruments are not particularly appropriate for a non-technically trained person to assess possibly dangerous exposure levels, however, for several reasons. First, such devices are typically expensive, and require at least some rudimentary training in electromagnetic field theory in order to use them properly. Secondly, a layperson typically cannot readily determine which exposure levels are acceptable, since absolute flux density measurements must be related in some manner to each of the frequency bands in which the radiation is observed.
Certain characteristics of the radiation of interest further complicate such measurements. Electromagnetic radiation in the ELF and VLF bands tends to be highly directional, may often vary greatly in magnitude over small distances, and may comprise magnetic fields having peak intensities are several orders of magnitude below that of the fields generated by the earth itself. Together, these and other considerations conspire to deprive the average individual of the ability to determine whether or not his or her own long-term exposure to electromagnetic radiation is an acceptable health risk.
What is needed is a user-friendly device enabling an average individual to easily determine whether the exposure to electromagnetic radiation in a particular situation is acceptable. The device would measure the exposure to electromagnetic flux densities in both an ELF band, centered around the common 60 hz alternating current (AC) power frequency, as well as the exposure to electromagnetic flux densities in a higher frequency VLF band, associated with emissions from electrical and electronic equipment such as VDTs, television sets, electric razors, hair dryers and the like.
The device should not require the user to determine field strength measurements in absolute numbers, but rather should provide a simple visual indication to indicate whether the exposure is well below acceptable radiation threshold levels, approaching the acceptable levels, or above the acceptable levels.
The visual indication should also automatically summarize detected variations in each of the frequency bands of interest, thereby further simplifying use of the device.